This invention relates generally to high voltage circuit breakers, and more specifically to methods and systems for analyzing circuit breaker contacts.
During testing of at least some known circuit breakers, a plurality of circuit breaker parameters may be monitored to facilitate determining whether the circuit breaker is operating as designed. One such parameter may be a circuit breaker contact pair status, which may indicate whether the contacts are opened or closed, and an analog position of the circuit breaker contacts.
Timing the main contact and auxiliary contacts may also be indicative of each contact's state. At least some known contacts are timed by inducing a small DC current into a first of the pair of contacts and detecting the current at a second of the contact pair. In one embodiment, the DC current may be recorded such that a current trace may be used to determine the timing of each contact. In an alternative embodiment, the presence or absence of the DC current may be used to start and stop timers to facilitate directly measuring the contact timing. Circuit breaker contact analog position and contact motion may be determined applying a mechanical transducer to the circuit breaker contact mechanism to transfer a motive force to a movable contact of the contact pair.
A high voltage circuit breaker when removed from service for maintenance, testing, or other reason may be grounded on both sides for personnel safety precautions. Circuit breaker contact timing measurements may be affected by induced currents, voltages, or other disturbances in a high voltage environment where circuit breaker measurement typically is performed. Moreover, such disturbances may limit the effectiveness and/or portability of the test equipment. In addition, motion measurement may be complicated by mechanical difficulties when mounting the transducer to the circuit breaker and when measuring rapid mechanical acceleration during circuit breaker operation. Additionally, the material used in fabricating the circuit breaker contact may also adversely affect the timing result.
At least some known circuit breaker designs use contact materials which have a relatively higher contact resistance, such as, for example, graphite, to protect the contact surface from wear during contact arcing. Furthermore, at least some known timing techniques require the removal of grounding cables from the circuit breaker being tested to facilitate enhancing the accuracy of the results. However, removing the grounding cables may reduce an amount of protection provided against injuries that grounding cables provide.